This invention relates to a recording medium comprising a phosphorus-containing fluorocarbon compound as lubricant.
Magnetic disk drives, magnetic hard disks or magnetic optical disks, are devices well known to one skilled in the art for storing information. The devices can use a rotatable thin film magnetic media with data tracks, a read/write transducer for reading/writing the information on the tracks, a slider for holding the transducer to the tracks, and a flying mode above the media. Ideally, the slider can fly as close as possible to the media leaving small spacing to allow the transducer to distinguish between the magnetic field from the closely spaced regions on the disk. During operation, the transducer head slides against the surface of the disk as the disk begins to rotate. The transducer head, when the disk reaches a predetermined rotational speed, floats in air at a predetermined distance from the surface of the disk. When the operation of the disk drive terminates, the transducer head begins to slide against the surface. Such sliding repeats every time the head and disk assembly is driven.
To maintain the slider as close as possible to the media or the transducer head as close to its recording surface as possible to minimize the flying height of the head, it requires a smooth recording surface. However, excessive stiction (static coefficient of friction) and friction can result if the head surface and the recording surface are too flat. Excessive stiction and friction can cause wear to the head and recording surfaces.
A phosphorus-containing high molecular weight perfluoroalkylpolyether compound has been used as a disk drive lubricant as disclosed in U.S. Pat. No. 5,874,169.
There is a continuing need to lubricate or coat the thin film disks and sliders to ensure the regular transducer fly height. There is also a need to develop a lubricant or coating that is stable at the operating conditions of the disks as well as during the manufacture of magnetic recording media.
The invention provides a recording medium comprising a phosphorus-containing fluorocarbon compound. The phosphorus-containing fluorocarbon compound can be an esterified phosphorus compound, a salt thereof, or combinations thereof.
Generally, a recording medium includes a magnetic medium (hard or flexible), magneto-optical medium, optical medium, or combinations thereof and can include either audio or video tape. A magnetic recording medium can comprise a magnetic layer on a non-magnetic substrate. The magnetic layer can comprise a protective overcoat on the magnetic layer. A lubricant can be present as a lubricant topcoat on the magnetic layer or on the protective overcoat, if present. The lubricant or lubricant topcoat comprises, consists essentially of, or consists of the phosphorus-containing fluorocarbon compound. The non-magnetic substrate, the magnetic layer, and the protective overcoat are well known to one skilled in the art. See, for example, U.S. Pat. No. 5,874,169, disclosure of which is incorporated herein by reference. Therefore the description of the non-magnetic substrate, the magnetic layer, and the protective overcoat is omitted herein for the interest of brevity. The invention disclosed herein is suitable for all recording media.
According to the invention, a magnetic recording medium comprising a phosphorus-containing fluorocarbon compound is provided. The phosphorus-containing fluorocarbon compound can be used as lubricant or as an additive to a lubricant. The phosphorus-containing fluorocarbon compound can be an esterified aryl phosphorus compound, a salt thereof, or combinations thereof.
The esterified aryl phosphorus compound can be a perfluoropolyether- or perfluoroalkyl-containing and phosphorus-containing aryl compound selected from the group consisting of Classes A, B, and C, and combinations of two or more thereof.
The Class A compound can be a perfluoropolyether- or perfluoroalkyl-containing and phosphorus-containing compound selected from the group consisting of partially esterified aryl phosphates, partially esterifled aryl phosphonates, and salts thereof, containing either (i) a mono-alkylene oxide or poly-alkylene oxide or phenylene oxide linking group between the phosphorus and a fluorocarbon group, or (ii) no linking group between the phosphorus and fluorocarbon group, and (iii) combinations of (i) and (ii). Representative compounds within Class A are shown below.
Class A(i) compounds having a mono- or poly-alkylene oxide linking group include those having formulae I, II, III, or combinations of two or more thereof.
[Rfxe2x80x94Yxe2x80x94](2xe2x88x92x)xe2x80x94P(E)xe2x80x94[ObC6R5][OM]xxe2x80x83xe2x80x83(Formula I)
[Rfxe2x80x2xe2x80x94Yxe2x80x94](2xe2x88x92x)xe2x80x94P(E)xe2x80x94[ObC6R5][OM]xxe2x80x83xe2x80x83(Formula II)
[MO]x[C6R5Ob](2xe2x88x92x)xe2x80x94P(E)xe2x80x94Yxe2x80x94Rfxe2x80x3xe2x80x94Yxe2x80x94P(E)xe2x80x94[ObC6R5](2xe2x88x92x)[OM]xxe2x80x83xe2x80x83(Formula III)
where:
Y is (CH2)zO(CH2CH2O)zxe2x80x2, wherein z is 1 to 4 and zxe2x80x2 is 0, 1 or 2, or Y is C6R4,
x is 0.05 to 1,
E is oxygen or sulfur,
b is 0 or 1,
R is the same or different substituent chosen from hydrogen, halogen, alkyl, aryl, nitro, cyano, alkoxy, primary and secondary amino, sulfonyl, carboxyl, or phenoxy, and
M is hydrogen, alkali metal, alkaline earth metal, or ammonium.
Rf is a polyether chain having a molecular weight ranging from 400 to 15,000 and composed of repeating units selected from the group consisting of:
Jxe2x80x94Oxe2x80x94(CF(CF3)CF2O)cxe2x80x94(CFXO)dxe2x80x94CFZ where:
J is a fluoroalkyl group selected from the group consisting of CF3, C2F5, C3F7, CF2Cl, C2F4Cl, and C3F6Cl,
X is xe2x80x94F or xe2x80x94CF3,
Z is xe2x80x94F, xe2x80x94Cl or xe2x80x94CF3, and
c and d are numbers such that the c/d ratio ranges from 0.01 to 0.5, and the molecular weight ranges from 400 to 15,000;
J1xe2x80x94Oxe2x80x94(CF2CF2O)exe2x80x94(CF2O)fxe2x80x94CFZ1 where:
J1 is a fluoroalkyl group selected from the group consisting of CF3, C2F5, CF2Cl, and C2F4Cl,
Z1 is xe2x80x94F or xe2x80x94Cl, and
e and f are numbers such that the e/f ratio ranges from 0.5 to 2 and, the molecular weight ranges from 400 to 15,000;
J2xe2x80x94Oxe2x80x94(CF(CF3)CF2O)jxe2x80x94CF(CF3) where:
J2 is C2F5 or C3F7, and
j is a number such that the molecular weight ranges from 400 to 15,000;
J3xe2x80x94Oxe2x80x94(CQZ2xe2x80x94CF2CF2xe2x80x94O)kxe2x80x94CQZ2xe2x80x94CF2 where:
J3 is selected from the group consisting of CF3, C2F5, and C3F7,
Q and Z2, equal or different, are F, Cl or H, and
k is a number such that the molecular weight ranges from 400 to 15,000;
J4xe2x80x94Oxe2x80x94(CF2CF2O)1xe2x80x94CF2 where:
J4 is CF3, or C2F5 and
1 is a number such that the molecular weight ranges from 400 to 15,000;
J5xe2x80x94(CF(CF3)CF2O)gxe2x80x94(CF2CF2O)hxe2x80x94(CFXxe2x80x94O)ixe2x80x94CFZxe2x80x94 where:
X and Z are as defined above, and
g, h and i are numbers such that (g+h) ranges from 1 to 50, the i/(g+h) ratio ranges from 0.1 to 0.05, and the molecular weight is from 400 to 15,000;
Rfxe2x80x2 is Z2xe2x80x94(CF2)m where:
Z2 is H, F, or Cl, and
m has a value from 2 to 20; and
Rfxe2x80x3 is a perfluoropolyether chain having a number average molecular weight of 500 to 15,000, selected from the group consisting of:
(i) (CF2CF2O)nxe2x80x94(CF2O)oxe2x80x94CF2 
xe2x80x83wherein the units with formulae C2F4O and CF2O are randomly distributed along the chain, and n and o are integers, whose ratio, n/o, is in the range of from 0.3 to 5;
(ii) (C3F6O)pxe2x80x94(CF2CF2O)qxe2x80x94(CFXO)rxe2x80x94CF2 wherein
X is F or CF3 and
p, q and r are numbers such that (p+q) ranges from 1 to 50, and the r/(p+q) ratio ranges from 0.1 to 0.05, and the molecular weight is from 400 to 15,000;
(iii) ((CQZ2)CF2CF2O)sxe2x80x94CF2xe2x80x94CF2 where
Q and Z2, equal or different, are F, Cl or H, and s is a number such that the molecular weight ranges from 400 to 15,000; and
(iv) (CF2O)xe2x80x94(CF2CF2O)txe2x80x94CF2 where t is a number such that the molecular weight ranges from 400 to 15,000.
Representative compounds within Class A(i) include:
For Formula I: F(CF(CF3)CF2O)nCF(CF3)CH2OP(O)[OH]C6H5 and
F(CF(CF3)CF2O)nCF(CF3)CH2OP(O)[OH]OC6H5 where n is 4 to 10.
For Formula II: F(CF2)mCH2CH2OP(O)[OH]C6H5 and F(CF2)mCH2CH2OP(O)[OH]OC6H5 where m is 4, 6 or 8.
For Formula III: [HO](C6H5)P(O)OCH2xe2x80x94(CF2CF2O)nxe2x80x94(CF2O)oxe2x80x94CF2xe2x80x94CH2OP(O)(C6H5)[OH] and
[HO](H5C6O)P(O)OCH2xe2x80x94(CF2CF2O)nxe2x80x94(CF2O)oxe2x80x94CF2xe2x80x94CH2OP(O)(OC6H5)[OH] where (n+o)=8 and n/o=1.
Class A(ii) compounds having no mono or poly alkylene or phenylene oxide linking group include those having formulae IV, V, VI, and combinations of two or more thereof.
[Rfxe2x80x94](2xe2x88x92x)xe2x80x94P(E)xe2x80x94[Obxe2x80x94C6R5][OM]xxe2x80x83xe2x80x83(Formula IV)
xe2x80x83[Rfxe2x80x2xe2x80x94](2xe2x88x92x)xe2x80x94P(E)xe2x80x94[ObC6R5][OM]xxe2x80x83xe2x80x83(Formula V)
[MO]x[C6R5Ob](2xe2x88x92x)xe2x80x94P(E)xe2x80x94Rfxe2x80x3xe2x80x94P(E)xe2x80x94[ObC6R5](2xe2x88x92x)[OM]xxe2x80x83xe2x80x83(Formula VI)
wherein Rf, Rfxe2x80x2, Rfxe2x80x3, x, E, b, R, and M are as previously defined for Formulae I to III.
Representative compounds within Class A(ii) include:
For Formula IV: F(CF(CF3)CF2O)nCF(CF3)P(O)[OH]C6H5 and F(CF(CF3)CF2O)nCF(CF3)P(O)[OH]OC6H5 where n is 4 to 10.
For Formula V: F(CF2)mP(O)[OH]C6H5 and F(CF2)mP(O)[OH]OC6H5 where m is 4, 6 or 8.
For Formula VI: [HO](C6H5)P(O)xe2x80x94(CF2CF2O)nxe2x80x94(CF2O)oxe2x80x94CF2xe2x80x94P(O)(C6H5)[OH] and [HO](H5C6O)P(O)xe2x80x94(CF2CF2O)nxe2x80x94(CF2O)oxe2x80x94CF2xe2x80x94P(O)(OC6H5)[OH] where (n+o) is 8, and n/o is 1.
The Class B compound can be an asymmetrical perfluoropolyether- or perfluoroalkyl-containing and phosphorus-containing compound being either (i) aryl phosphites or aryl phosphates containing a mono-alkylene oxide or poly-alkylene oxide or phenylene oxide linking group between the phosphorus and a perfluoroether group, or (ii) aryl phosphines, aryl phosphinites, aryl phosphonites, aryl phosphine oxides, aryl phosphinates or aryl phosphonates with no linking group between the phosphorus and a fluorocarbon group, or (iii) combinations of (i) and (ii). Representative compounds within Class B have the following formulae.
Class B(i) compounds having a mono- or poly-alkylene oxide linking group include formulae VII, VIII, or combinations thereof.
[Rfxe2x80x94Yxe2x80x94](3xe2x88x92y)xe2x80x94P(E)axe2x80x94[Oxe2x80x94C6R5]yxe2x80x83xe2x80x83(Formula VII)
(C6R5O)2xe2x80x94P(E)axe2x80x94Yxe2x80x94Rfxe2x80x3xe2x80x94Yxe2x80x94P(E)axe2x80x94(OC6R5)2xe2x80x83xe2x80x83(Formula VIII)
wherein R, Rf, Y, and E are as previously defined and y is 0.05 to 2, and a is 0 or 1.
Class B(ii) compounds having no polyalkylene oxide linking group include those having the formulae Ix, X, IX, or combinations of two or more thereof.
[Rf](3xe2x88x92y)xe2x80x94P(E)axe2x80x94[ObC6R5]yxe2x80x83xe2x80x83(Formula IX)
[Rfxe2x80x2](3xe2x88x92y)xe2x80x94P(E)axe2x80x94[ObC6R5]yxe2x80x83xe2x80x83(Formula X)
[C6R5O]2xe2x80x94P(E)axe2x80x94Rfxe2x80x3xe2x80x94P(E)axe2x80x94[ObC6R5]2xe2x80x83xe2x80x83(Formula XI)
wherein Rf, Rfxe2x80x2, Rfxe2x80x3, a, b, E, R, y, and n are as previously defined for Formulae I to VIII.
Representative compounds within Class B(i) include:
For Formula VII: [F(CF(CF3)CF2O)nCF(CF3)CH2O]P(OC6H5)2 and
[F(CF(CF3)CF2O)nCF(CF3)CH2O]2P(O)(OC6H5) where n is 4 to 10.
For Formula VIII: (H5C6O)2Pxe2x80x94(CF2CF2O)nxe2x80x94(CF2O)oxe2x80x94CF2xe2x80x94P(OC6H5)2 and (H5C6O)P(O)xe2x80x94(CF2CF2O)nxe2x80x94(CF2O)oxe2x80x94CF2xe2x80x94P(O)(OC6H5)2 where n is (n+o) is 8, and n/o is 1.
Representative compounds within Class B(ii) include:
For Formula IX: F(CF(CF3)CF2O)nCF(CF3)P(C6H5)2, [F(CF(CF3)CF2O)nCF(CF3)]2P(OC6H5), [F(CF(CF3)CF2O)nCF(CF3)]P(O)(C6H5)2, and [F(CF(CF3)CF2O)nCF(CF3)]2P(O)(OC6H5) where n is 4 to 10.
For Formula X: F(CF2)mP(C6H5)2, [F(CF2)m]2P(OC6H5), F(CF2)mP(OC6H5)2, [F(CF2)m]P(O)(C6H5)2, [F(CF2)m]2P(O)(OC6H5), and F(CF2)mP(O)(OC6H5)2 where m is 4, 6, or 8.
For Formula XI: (H5C6)2Pxe2x80x94(CF2CF2O)nxe2x80x94(CF2O)oxe2x80x94CF2xe2x80x94P(C6H5)2, (H5C6O)2Pxe2x80x94(CF2CF2O)nxe2x80x94(CF2O)oxe2x80x94CF2xe2x80x94P(OC6H5)2, (H5C6)2P(O)xe2x80x94(CF2CF2O)nxe2x80x94(CF2O)oxe2x80x94CF2xe2x80x94P(O)(C6H5)2, and (H5C6O)2P(O)xe2x80x94(CF2CF2O)nxe2x80x94(CF2O)oxe2x80x94CF2xe2x80x94P(O)(OC6H5)2 where (n+o) is 8; and n/o is 1.
Class C compound can be a perfluoropolyether- or perfluoroalkyl-containing and phosphorus-containing compound selected from the group consisting of partially esterified phosphates, phosphonates, and salts thereof, containing either (i) a mono- or poly-alkylene oxide or phenylene oxide linking group between the phosphorus and a fluorocarbon group, or (ii) no linking group between the phosphorus and fluorocarbon group.
Representative compounds within Class C include compounds having the formulae XII to XIV shown below.
[Rfxe2x80x94Yxe2x80x94](3xe2x88x92x)xe2x80x94P(E)xe2x80x94[OM]xxe2x80x83xe2x80x83(Formula XII)
[Rfxe2x80x2xe2x80x94Yxe2x80x94](3xe2x88x92x)xe2x80x94P(E)xe2x80x94[OM]xxe2x80x83xe2x80x83(Formula XIII)
[Rfxe2x80x94Yxe2x80x94](2xe2x88x92x)xe2x80x94[MO]xxe2x80x94P(E)xe2x80x94Yxe2x80x94Rfxe2x80x3xe2x80x94Yxe2x80x94P(E)xe2x80x94[OM]xxe2x80x94[Yxe2x80x94Rf](2xe2x88x92x)xe2x80x83xe2x80x83(Formula XIV)
where Y, x, R, Rf, Rfxe2x80x2, Rfxe2x80x3, M and E are the same as described above.
Representative compounds within Class C(i) include:
For Formula XII: F(CF(CF3)CF2O)nCF(CF3)CH2OP(O)[OH]2 and [F(CF(CF3)CF2O)nCF(CF3)CH2O]2P(O)[OH] where n is 4 to 10.
For Formula XIII: F(CF2)mCH2CH2OP(O)[OH]2 and [F(CF2)mCH2CH2O]2P(O)[OH] where m is 4, 6 or 8.
For Formula XIV: [HO]2P(O)OCH2xe2x80x94(CF2CF2O)nxe2x80x94(CF2O)0xe2x80x94CF2xe2x80x94CH2OP(O)[OH]2 and 
where (n+o)=8 and n/o=1 and j=4 to 10.
Class C(ii) compounds do not have a mono- or poly-alkylene oxide or phenylene linking group and can be represented by formulae XV to XVII shown below.
[Rfxe2x80x94](3xe2x88x92x)xe2x80x94P(E)[OM]xxe2x80x83xe2x80x83(Formula XV)
[Rfxe2x80x2xe2x80x94](3xe2x88x92x)xe2x80x94P(E)xe2x80x94[OM]xxe2x80x83xe2x80x83(Formula XVI)
[Rfxe2x80x94](2xe2x88x92x)xe2x80x94[MO]xxe2x80x94P(E)xe2x80x94Rfxe2x80x3xe2x80x94P(E)xe2x80x94[OM]x[xe2x80x94Rf](2xe2x88x92x)xe2x80x83xe2x80x83(Formula XVII)
wherein Rf, Rfxe2x80x2, Rfxe2x80x3, x, E, and M are as previously defined.
Representative compounds within Class C(ii) include:
For Formula XV: F(CF(CF3)CF2O)nCF(CF3)P(O)[OH]2 and [F(CF(CF3)CF2O)nCF(CF3)]2P(O)[OH] where n is 4 to 10.
For Formula XVI: F(CF2)mP(O)[OH]2 and [F(CF2)m]2P(O)[OH] where m is 4, 6 or 8.
For Formula XVII: [HO]2P(O)xe2x80x94CF2Oxe2x80x94(CF2CF2O)nxe2x80x94(CF2O)oxe2x80x94CF2xe2x80x94P(O)[OH]2 and 
where (n+o) is 8, and n/o is 1 and j=4 to 10.
The above-disclosed compounds can be produced by any methods known to one skilled in the art. The following disclosure shows some examples for synthesizing these compounds.
For compounds of Classes A(i) and B(i), the syntheses of can be accomplished by the method described by Moreton in U.S. Pat. No. 2,694,083, disclosure of which is incorporated herein by reference. Briefly, the synthesis can be carried out by reaction of either (a) aryloxy substituted or aryl substituted phosphorus oxychlorides at elevated temperatures with a fluoroalcohol of the formula Rfxe2x80x94OH, or (b) with the corresponding fluoroalkyi phosphorus dichloride and a substituted phenol in which Rf is the same as that disclosed above. Alternately, the compounds can be produced by mixing the reactants in the presence of a dry aprotic organic base such as triethylamine or pyridine, and allowing the reaction to proceed at room temperature until complete either with or without solvent as described by Paciorek in U.S. Pat. No. 5,550,277. Control over the specific reaction products is by stoichiometry. This reaction is followed by hydrolysis to form the corresponding acid ester. Additionally, the products are neutralized with a solution or suspension of the hydroxide or carbonate of the alkali metal or alkaline earth metal, or ammonium hydroxide solution, prior to isolation to provide the corresponding salt, producing a rust and corrosion prevention additive compatible with perfluoropolyether oils and greases containing sodium nitrite. The solution is washed with water to remove excess acid and salts or base and salts, then vacuum stripped to remove solvents and volatiles.
Compounds of Classes A(ii) and B(ii) can be produced by contacting a perfluoroalkyl or perfluoroether iodide with elemental phosphorus at an elevated temperature to produce a diiodophosphine, which can then be contacted with either a metalated aryl or aryloxy compound to produce the corresponding phosphorus(III) compounds; or oxidized with chlorine/water or hydrogen peroxide to produce the phosphorus(V) oxide. The phosphorus(III) can be oxidized with chlorine followed by treatment with H2S or Na2S to produce the thiophosphorus(V) materials.
Because each of the above-disclosed reactions is well known to one skilled in the art, the descriptions are omitted herein.
The phosphorus-containing fluorocarbon compound preferably has a molecular weight of between about 500 and about 100,000, more preferably between 1,000 and 6,000.
The viscosity of the phosphorus-containing fluorocarbon compound is preferably sufficient to minimise capillary action of the lubricant between the surface of the substrate and the disk head. The viscosity of the phosphorus-containing fluorocarbon compound is preferably between about 1 and 1000 cP (0.001 and 1 Pa.s) in the temperature range of about 0xc2x0 C. to about 85xc2x0 C.
The phosphorus-containing fluorocarbon compound can also be used as an additive for the recording medium. The phosphorus-containing fluorocarbon compound can be diluted in a solvent before it is applied to the disk. Any solvent having a vapour pressure that can readily evaporates at ambient temperature and pressure can be used. Examples of such solvent can include a commercially available fluorocarbon, hydrofluorocarbon, perfluorocarbon, or combinations of two or more thereof The concentration of the phosphorus-containing fluorocarbon compound in the solvent, if used, can be from about 0.0001 to about 99% by weight
An impurity, if present, is preferably removed from the phosphorus-containing fluorocarbon compound before the phosphorus-containing fluorocarbon compound is applied to the recording medium. The removal, if required, can be carried out by, for example, ultrafiltration with a filter of, for example, 0.2 xcexcm. During filtration, the phosphorus-containing fluorocarbon compound can be dissolved in a solvent. Following filtration, the solvent can be removed by any means known to one skilled in the art such as, for example, evaporation, and can be recycled/re-used.
The phosphorus-containing fluorocarbon compound can be applied to the magnetic recording medium by any means known to one skilled in the art such as, for example, dip coating, spraying, spin coating or vapor deposition. The pulling-up speed, the density of the phosphorus-containing fluorocarbon compound and the surface tension are relevant for determining the film thickness of the phosphorus-containing fluorocarbon compound. See xe2x80x98Dip-Coating of Ultra-Thin Liquid Lubricant and its Control for Thin-Film Magnetic Hard Disksxe2x80x99 in IEEE Transactions on Magnetics, vol. 31, no. 6, November 1995, for further details.
The lubricant can be applied to a thickness of less than about 300 nm, and most preferably a thickness of about 100 nm to about 300 nm.
Bonding of the lubricant to the magnetic recording medium can be improved by removing impurities from the surface of the recording medium. Impurities can be removed from the surface of the recording medium using a mild oxygen plasma or an isopropanol vapor rinse. However, less cleaning of the surface of the recording medium is required when using the lubricant of the present invention.